What are the sources for BAC calculations?

The Widmark rearrangement, r = 0.68 for men and 0.55 for women, density 0.8, and the 0.015 g/100 mL per hour example are from the Washington State Patrol worksheet Widmark’s Equation (R.G. Gullberg, 3 March 2002), https://wsp.wa.gov/breathtest/docs/webdms/Studies_Articles/Widmarks%20Equation%2003-07-2002.pdf. One U.S. standard drink as 0.6 fl oz or about 14 grams is from NIAAA, What Is A Standard Drink?, https://www.niaaa.nih.gov/alcohols-effects-health/overview-alcohol-consumption/what-standard-drink.

BAC Calculator

Widmark estimate from drinks, alcohol percent, volume, weight, sex, and hours. An estimate, not a diagnosis.

Body weight

Drink volume

Number of drinks *

Alcohol percent *

Volume of one drink (fl oz) *

Body weight (lb) *

Sex *

Hours since first drink *

Smart Tips

• Count the alcohol percent and the volume of each drink. A 12 fl oz beer at 5% is not the same as a 12 fl oz beer at 8%.

• NIAAA describes one U.S. standard drink as about 0.6 fl oz, or about 14 grams, of ethanol.

• The Widmark line uses r = 0.68 for men and r = 0.55 for women, and subtracts 0.015 g/100 mL per hour.

• Food, medications, and a different elimination rate are not in this arithmetic.

• A result at or below zero is shown as 0. That is the line going through zero, not a breath reading.

• Do not use this number to decide whether to drive.

The Formula

BAC (g/100 mL) = 100 × [(ethanol fl oz × 0.8) / (weight oz × r) − 0.00015 × hours]

r 0.68 men, 0.55 women
Widmark factor, L/kg

0.8 Ethanol density in the worksheet
Mass ounces per fluid ounce

0.015 Elimination per hour
g/100 mL, example 1 of the worksheet

0.6 One NIAAA standard drink
Fluid ounces of ethanol, counted separately

Weight in ounces is pounds × 16. A negative line is shown as 0. This is not a state limit and not a breath test.

Key Insights

Not a breath test

The figure is Widmark arithmetic. It is not a breath, blood, or urine result, and it will not match a police test.

Do not drive from it

Do not use this result to decide whether to drive, ride, or operate anything. No state limit is shown on this page.

Two published rates

The worksheet’s first example uses 0.015 g/100 mL per hour. Its second example uses 0.017 to show that the rate is not one number for every person. This page uses 0.015.

Standard drinks are separate

The standard-drink count divides ethanol fluid ounces by 0.6, the NIAAA description. It is not the Widmark result.

Medical Disclaimer

Not a breath test: This is a Widmark estimate, not a breath, blood, or urine test. Do not drive from this result.

Estimate only: This page is an estimate, not a diagnosis, a lab test, or a treatment plan.

Not legal advice: This page does not show a state driving limit and does not say whether a person is impaired.

Frequently Asked Questions

It is the Widmark estimate in grams per 100 mL, which is the same number people read as a percent. It uses the drinks, strength, volume, weight, sex, and hours you enter. It is not a breath test.

Men use r = 0.68 and women use r = 0.55. The page subtracts 0.015 g/100 mL for each hour since the first drink. Those are the constants in the Washington State Patrol Widmark worksheet’s first example. The worksheet’s second example uses 0.017 to show a different rate. This page does not switch rates.

NIAAA describes one U.S. standard drink as about 0.6 fluid ounces, or about 14 grams, of pure alcohol. That is the amount in 12 fl oz of 5% beer, 5 fl oz of 12% wine, or 1.5 fl oz of 40% spirits. The standard-drink line divides your ethanol fluid ounces by 0.6. The Widmark line uses the worksheet density of 0.8, not a separate 14-gram conversion.

No. Do not drive from this result. The page does not show a state limit, and the number is not a breath test. Food, medicines, and a personal elimination rate are not in the formula.

The worksheet subtracts the elimination rate for every hour. If that subtraction passes zero, the page shows 0. A zero on this page is not a laboratory result and does not mean it is safe to drive.

The Widmark rearrangement, r = 0.68 for men and 0.55 for women, density 0.8, and the 0.015 g/100 mL per hour example are from the Washington State Patrol worksheet Widmark’s Equation (R.G. Gullberg, 3 March 2002), Widmark’s Equation. One U.S. standard drink as 0.6 fl oz or about 14 grams is from NIAAA, What Is A Standard Drink?.

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Note:Not a breath test. Do not drive from this result. The figure uses r 0.68 or 0.55, density 0.8, and 0.015 g/100 mL per hour. It is an estimate, not a diagnosis or a legal finding.